This invention relates to a water-based mineral stain for wood and other substrates. More specifically, the invention relates to a process in which a metal salt and an oxygen source react with the substrate to provide a stable color or other desired effect such as preserving the substrate.
Many commercial stains readily available on the market are oil or solvent-based and/or contain hazardous chemicals subject to increasing environmental regulation and health concerns. There is a growing need for water-based colorants and finishes that contain no hazardous chemicals. Federal and state initiatives are leading to bans on stains using volatile organic compounds (e.g. petroleum, mineral spirits, toluene, or benzene).
Most water-based products for coloring and finishing wood and other materials are primarily based upon a pigment or dye suspended in a binder such as acrylic resin, which is spread onto the wood surface and held in place by the binder. Such products, although less toxic, exacerbate a problem of all conventional stains, namely that while coloring a wood such as pine they sink in more deeply into the soft pulp and are repelled by the harder wood around the annual growth rings formed during the dormant period in a tree's growing season. For example, stains such as Minwax™ can color pine to a maple-like general color, but in doing so emphasize the distinctive grain-markings characteristic of pine. Such products tend to produce marginal results and an uneven staining pattern. There would be great advantages for a stain capable of coloring both hard and soft woods evenly allowing for a maple-like overall color with a much more subtle grain pattern, thereby allowing a soft wood to mimic the appearance of a hard wood more effectively. Also, water-based stains tend to raise wood grain, requiring additional sanding.
There is a need for a coloring process having the environmental benefit of allowing rapidly growing, sustainably harvestable woods such as pine and other fast-growing and therefore “renewable” wood resources to give the visual appearance of endangered hardwoods such as mahogany, ebony, redwood, and other species that are increasingly rare and expensive.
The construction, furniture, and woodworking industries need new improved water-based stains effective for soft woods. Likewise, there is a need for environmentally beneficial coloring processes for wood products such as paper and cardboard, for fabrics for clothing and upholstery, and for manufactured polymer products.
Conventional stains take a relatively long time to dry and can only be applied in temperatures at or above 55 degrees F. There is a need for a stain that can be applied outside this range, for example, for exterior woodwork in a colder climate.
Conventional stains are made up of a binder and a pigment or dye. Many of these coloring agents are “fugitive,” fading over time, especially in exterior settings. A stable coloring agent that is permanent and does not fade over time and even becomes richer and slightly darker would be an improvement over conventional stains.
Conventional stains can be used on dry, cured wood only. There is a need for stains that can be applied to damp or “green” un-cured wood. Conventional stains coat the surface of aromatic woods such as cedar, preventing the natural aroma from being released by the wood. There are advantages to stains that leave a wood fully aromatic. Oil-based conventional stains can be difficult to over-coat with water-based acrylic finishes. A stain that can be over-coated with any type of oil or water-based finish would have pronounced advantages.
Stains used to simulate wood aging, such as Cabot Stains Bleaching Oil (TM) can only be used for exterior use and the appearance of aging of the wood takes many months from application. An aging treatment that can be used indoors and occurs immediately has clear advantages. Other aging processes require the use of harsh acids, bleaches and other toxic chemicals and require complex manual wood-distressing techniques such as multiple layering of different stains to mimic grain patterns of aged wood. Preferable would be an aging treatment that is non-toxic and can be applied easily by a layman.
Some coloring processes have been developed to compensate for the unattractive green color of CCA (copper-chromium-arsenic) pressure-treated preserved lumber, such as Leach, U.S. Pat. Nos. 4,752,297 and 4,313,976. These processes rely on organic acids and other organic compounds. They are concerned primarily with preservation of wood, are able to produce only a limited color palate, and are not of general applicability.
A process of using an aqueous solution of an alkaline earth metal base to treat wood is described in Gaines et al. U.S. Pat. No. 4,757,154. This method requires immersing wood at high temperature and pressure and sanding to remove an unattractive deposit, so it is not a viable method for staining wood. Some woodworkers soak wood in a solution of iron-rich fertilizer to produce a dusty gray tone. The coloring is unstable, uneven, fades over time, leaches out if exposed to moisture, and if overcoated creates an unattractive residue, so it is not in regular use.